Size dependence of photocatalytic oxidation reactions of Rh nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) support

Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and solid-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photocatalytic water splitting, CO oxidation, and H2 oxidation. Mixed Ga–Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2–9 nm. These catalysts had negligible activity in photocatalytic H2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga–Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The influence of particle size on Rh-catalyzed oxidation of CO and H2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The opposite holds for H2 oxidation

Nitrogen-doping of bulk and nanotubular TiO2 photocatalysts by plasma-assisted atomic layer deposition

Plasma-assisted atomic layer deposition (PA-ALD) was adopted to deposit TiO2-xNx ultrathin layers on Si wafers, calcined Ti foils and nanotubular TiO2 arrays. A range of N content and chemical bond configurations were obtained by varying the background gas (O2 or N2) during the Ti precursor exposure, while the N2/H2-fed inductively coupled plasma exposure time was varied between 2 and 20 s. On calcined Ti foils, a positive effect from N doping on photocurrent density was observed when O2 was the background gases with a short plasma exposure time (5 and 10 s). This correlated with the presence of interstitial N states in the TiO2 with a binding energy of 400 eV (Ninterst) as measured by X-ray photoelectron spectroscopy. A longer plasma time or the use of N2 as background gas resulted in formation of N state with a binding energy of 396 eV (Nsubst) and very low photocurrents. These Nsubst are linked to the presence of Ti3+, which act as detrimental recombination centers for photo-generated electron-hole pairs. On contrary, PA-ALD treated nanotubular TiO2 arrays show no variation of photocurrent density (with respect to the pristine nanotubes) upon different plasma exposure times and when the O2 recipe was adopted. This is attributed to constant N content in the PA-ALD TiO2-xNx, regardless of the adopted recipe

Improved electrocatalytic activity of Pt on carbon nanofibers for glucose oxidation mediated by support oxygen groups in Pt perimeter

Support effects in supported metal catalysts are well studied for thermocatalytic reactions, but less studied for electrocatalytic reactions. Here, we prepared a series of Pt supported on carbon nanofiber catalysts which vary in their Pt particle size and the content of oxygen groups on the surface of the CNF. We show that the activity of these catalysts for electrocatalytic glucose oxidation relates linearly with the content of support oxygen groups. Since the electronic state of Pt (XAS) and Pt surface structure (CO-stripping) were indistinguishable for all materials, we conclude that sorption effects of glucose play a crucial role in catalytic activity. This was further confirmed by establishing a relation between the annulus of the Pt particles and the activity.</p

Thermally annealed AG nanoparticles on anodized aluminium oxide for SERS sending

In this paper we report a study of novel thermally stable surface enhanced Raman scattering (SERS) substrates consisting of Ag nanoparticles immobilized on an anodized aluminum oxide (AAO) support. The morphological and chemical characteristics and the SERS activity of the Ag nanoparticles before and after the thermal treatment were evaluated using SEM, XPS, UV-vis and Raman spectroscopy. Our results show that the nanoporous surface of AAO significantly hinders the fusion of Ag nanoparticles to single large particles at up to 400 °C, preserving high SERS enhancement. XPS and SERS results indicate that exposure to high temperatures efficiently ‘cleanses’ the surface from citrate remnants, opening more binding sites for analytes on Ag nanoparticles. In addition, thermal decomposition of silver oxide occurs at 400 °C, ensuring a pure metallic surface and further enhancing SERS activity

PTFE treatment by remote atmospheric Ar/O2 plasmas: a simple reaction scheme model proposal

Polytetrafluoroethylene (PTFE) samples were treated by a remote atmospheric pressure microwave plasma torch and analyzed by water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS). In the case of pure argon plasma a decrease of WCA is observed meanwhile an increase of hydrophobicity was observed when some oxygen was added to the discharge. The WCA results are correlated to XPS of reference samples and the change of WCA are attributed to changes in roughness of the samples. A simple kinetics scheme for the chemistry on the PTFE surface is proposed to explain the results

A new approach to silver-catalysed aerobic oxidation of octadecanol: probing catalysts utilising a flat, two-dimensional silicon-based model support system

Aerobic oxidation of a thin film of octadecanol at 105 °C and ambient pressures to its corresponding carbonyl derivatives (a mixture of aldehyde and carboxylic acid) was for the first time performed over a flat-model (i.e. two-dimensional), silicon wafer-supported metallic silver catalyst. The experimental set-up was extraordinary simple. An open-to-the-atmosphere glass beaker was used as reactor. Just enough octadecanol was placed on the silicon-supported catalytic surface to cover it with a thin film when melted. Reaction progress was monitored by ATR-FTIR analyses to identify the appearance of octadecanal and octadecanoic acid carbonyl stretching peaks at 1730 and 1710 cm- 1 respectively. The successful demonstration of this simple approach in studying catalysed small-molecule condensed organic reactions opens a new avenue towards simplified catalytic mechanistic studies of such processes. The catalyst was prepared by spin coating silver nitrate on a flat silicon wafer with (100) surface orientation, pretreated to have 4-5 silanol (SiOH) groups per nm2. Reduction by hydrogen at 350 °C afforded metallic silver particles on the two-dimensional support at a nominal surface concentration of ca. 21–23 silver atoms/nm2. XPS differentiation between the catalyst precursor, AgNO3, and the metallic silver catalytic surface required use of the Auger MNN kinetic energies. TEM studies of the active catalyst showed no serious aggregation of metallic Ag particles occurred during reduction

Size dependence of photocatalytic oxidation reactions of Rh nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) support

Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and solid-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photocatalytic water splitting, CO oxidation, and H2 oxidation. Mixed Ga–Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2–9 nm. These catalysts had negligible activity in photocatalytic H2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga–Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The influence of particle size on Rh-catalyzed oxidation of CO and H2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The opposite holds for H2 oxidation

Oxygen reduction kinetics on electrodeposited PtCo as a model catalyst for proton exchange membrane fuel cell cathodes: Stability as a function of PtCo composition

PtCo catalysts with composition varying between Pt80Co20 and Pt10Co90 were prepared by electrochemical underpotential codeposition. The bimetallic catalysts were subjected to 1000 electrochemical cycles in 0.5 M HClO4 at room temperature. The activity and stability of these electrodes for oxygen reduction was determined, in conjunction with the characterization of these catalysts with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Although Pt-rich electrodes had better activity in the initial stages of potential cycling, higher Co atomic ratios led to higher stability and higher oxygen reduction reaction (ORR) activity after electrochemical cycling. Pt10Co90 turned out to be the best electrode among the alloys considered, in terms of ORR activity and stability, which is linked to a higher concentration of Co on the surface

Supported Pt-Re catalysts for the selective hydrogenation of methyl and ethyl esters to alcohols

The effect of Re-addition to Pt/TiO2catalysts for the hydrogenation of carboxylic acids and esters to their corresponding alcohols was investigated. The highest catalytic activity was observed for the materials with Pt:Re molar ratio of 1:2, which allowed for a complete conversion of hexanoic acid under mild conditions. The hydrogenation of esters over the same catalysts was much more difficult. The reactions showed only moderate alcohol yields which also depended strongly on the alkoxy moiety of the ester substrate. The highest yield of ca. 25% was achieved by the hydrogenation of ethyl hexanoate. Conversion of methyl hexanoate was much less efficient. This was attributed to the inhibiting effect of methanol by-product. In situ FTIR spectroscopy suggests that the decarbonylation of methanol and the resulting CO poisoning of the catalyst surface in the course of the reaction is the most likely cause of the low activity of Pt and Pt-Re/TiO2towards methyl ester hydrogenation